With the advance of the rapid processing technique in recent years, rapid processing of a large amount of color photographic materials for prints has been achieved. And it has been strongly demanded that a light-sensitive material have a much stabler performance varying less within a lot or among lots in manufacturing as well as a capability of producing high quality images. Gradation reproduction is an important factor for obtaining light-sensitive material producing high quality images. The gradation can be divided into a foot part gradation ranging from low density part to medium density part, a linear part gradation ranging from medium density part to high density part, and a shoulder part gradation up to the highest density part, each of which is essential to gradation reproduction. Particularly, the linear part gradation is fundamental for gradation reproduction; therefore, a poor linearity may cause a fatal defect in gradation reproduction. Further, a light-sensitive material having a wide exposure latitude is demanded for the purpose of improving description of details In order to reconcile a proper gradation reproduction and a wide exposure latitude, a much higher maximum density (hereinafter referred to as Dmax) is required. Accordingly, there is a demand for a lightsensitive material which has a linear part gradation excellent in linearity and is capable of providing a high Dmax value. Though various approaches have been made to satisfy the requirement, there is much room left for improvement even now. For example, Japanese Pat. O.P.I. Pub. Nos. 225141/1985 and 225142/1985 propose to mix two different kinds of emulsions for improvement in gradation. This method, though effective in enhancing the linearity of a gradation, cannot provide an adequately high Dmax value; therefore, improvement of the linearity and enhancement of Dmax cannot be reconciled with each other by this method alone. Further, this method is not for stabilizing the manufacture of an emulsion.
Various efforts have been made in the art to improve the sensitivity of emulsions by use of spectral sensitizing dyes. For example, in Japanese Pat. O.P.I. Pub. No. 9653/1984, the emulsion stability is improved by adding spectral sensitizing dyes after the completion of chemical ripening; in Japanese Pat. O.P.I. Pub. No. 41849/1988, diminution in storage fog and prevention of soft gradation are attempted by adding spectral sensitizing dyes during the formation of silver halide grains. However, an emulsion chemically ripened directly after the formation of silver halide grains is different in gradation from an emulsion stored temporarily in a refrigerator after the formation of silver halide grains and then chemically ripened after few days; accordingly, these techniques cannot support the stable material supply in production, which the present invention aims at, and are not methods for raising a Dmax value. Though various improvements have been attempted as by the addition of spectral sensitizing dyes described above, it is not easy to control the use of spectral sensitizing dyes properly, and even small changes in addition time or addition temperature thereof often lead to large changes in performances thereof.
Japanese Pat. O.P.I. Pub. No. 125612/1983 discloses a technique to reduce fogs and improve the description of highlights by controlling the pAg and temperature during chemical ripening. However, this is a technique for improving the description of highlights by reducing the temperature, and not for obtaining a gradation high in linearity and Dmax value which the present invention aims at.
On the other hand, the speed-up of development has accelerated the spread of mini-laboratories engaged in rapid processing, and the processing pattern of light-sensitive materials has also come to change. There has so far been a demand for light-sensitive materials of which latent images are stable for 10 minutes to 24 hours or for the time interval between exposing and processing, and light-sensitive materials so-manufactured have been supplied. With the spread of mini-laboratories, however, stabilization of latent images in the very early stage, which covers several seconds to several minutes after exposing, has come to be the most important. Further, services of delivering finished prints on the spot to customers making trips to resorts, by utilizing the merit of mini-laboratories having a capability of rapid-processing have increased. This creates the necessity for light-sensitive materials less susceptible to temperature and humidity, because the control of temperature and humidity performed at ordinary processing laboratories cannot be carried out by mini-laboratories in resorts where temperature and humidity change with changes of the seasons.